I was making some waterglass foam today, just by heating up some liquid waterglass on aluminum foil in an aluminum-foil-covered steel bowl over a fire, and it occurred to me that maybe it’s possible to get the most crucial aspects of the structure of wood in a glass-fiber composite in a very simple way.
Specifically, I’m thinking that you ought to be able to soak a glass-fiber tow or stack of unidirectional cloths in waterglass, then bake it, just as I did without the fiber today. The waterglass will attack the glass-fiber tow at high temperatures, but I think the whole process can be done at a low enough temperature to keep that to a minimum. The result should or might be a glass composite material consisting of a lightweight foam holding together a lot of parallel fibers.
There are a number of potentially interesting aspects of this kind of composite, but the primary one that interests me is the combination of load-bearing capability with ease of mechanical shaping. In general, materials that can bear a lot of load, such as diamond, tungsten carbide, sapphire, quartz, steel, are also hard to shape mechanically. There are at least two ways to escape from this: post-shaping hardening (like concrete or heat treatments of steel, or casting), and foams.
Natural wood is a foam, with continuous parallel cellulose fibers connected together with lignin glue, plus lots of empty space. The empty space has several big advantages: it makes wood much easier to cut; it makes the wood much stiffer, like a sandwich panel; it inhibits crack propagation from one fiber to another, dramatically improving impact strength, because cracks perpendicular to fibers must propagate along a jagged zigzag path (“splintering”), greatly increasing the energy required; and it allows impacts to plastically deform the material without damaging fibers. (Bamboo is also a fiber-foam composite, but with a different structure; see DOI 10.1007/s00226-007-0127-8.)
Other solid foams, such as refractory firebrick, waterglass foam, styrofoam, and polyurethane cushions, are also much easier to shape than the corresponding bulk material would have been. Earlier tonight I cut through waterglass foam with a box cutter; I could push the unsupported blade all the way through 15 mm or more of foamed waterglass, corresponding to about 1 mm of solid glass, only because the particles displaced by the knife could move aside into the voids in the foam.
Ceramic-matrix composites get their improvement in impact strength by recruiting a longer section of crack-bridging fibers to elastically resist crack-widening movements than the section actually within the crack; this is enabled by weakening the bonding between the matrix and the fiber reinforcement. This seems closely analogous to the splintering behavior of natural wood, but I’m not sure it’s quite the same.
So my thesis is that maybe a composite of glass foam and glass fibers will be lightweight, rigid, easy to cut, and impact-resistant.
Alternative or supplementary fiber reinforcements might include steel, basalt, copper, carborundum, or carbon fiber.
If the foaming of the glass is to happen rapidly and uniformly, it would be helpful for the heat to be applied by a reaction within the mixture (so-called “self-propagating high-temperature synthesis”), but it is probably crucial that the direction of propagation of this reaction be at right angles to the fiber direction; if it is in the direction of the fibers it will not only stretch them but also kink them. For this purpose it might be helpful to lay the reagents into the foam in the form of “fibers” parallel to the structural fibers, so that the reaction can propagate very rapidly along each “fiber” but much more slowly from one “fiber” to another; to make these reagent “fibers” hollow; and to apply the initial ignition simultaneously along the whole length of the material. SHS could perhaps be usefully applied to higher-temperature glass foaming reactions which might yield stronger and more water-resistant foams than waterglass; the conventional one seems to be reacting manganese dioxide with carbon in a matrix of soda-lime glass, but many others are possible.